Basis Of Discrete Element Method Research Articles

Numerical method for thixotropic behavior of fresh concrete

The thixotropic characteristic or rest & shearing time–dependence of fluidity of fresh concrete has an influence on its production and construction processes. In this paper, the mechanisms of the thixotropy and rest & shearing time-dependence were discussed, followed by proposing an analytical approach to numerical prediction of the rest & agitating time-dependent flow behaviors on the basis of Discrete Element Method (DEM). In this new DEM, the effects of cement hydration, physical flocculation of cementitious particles, and agitation were taken into account. To validate the numerical method, the rheological tests of fresh mortars with or without mineral admixtures were performed after the mortar samples stood still for different times, using the B-type viscometer, of which the rotor’s rotation would break down its surrounding particles’ flocculation structure. The numerical results of toque-rotational speed relationship were close to the experimental results.

Tensile test simulation of high-carbon steel by discrete element method

Purpose – The tensile test is one of the fundamental experiments used to evaluate material properties. Simulating a tensile test can be a replacement of experiments to determine mechanical parameters of a continuous material. The paper aims to discuss these issues. Design/methodology/approach – This research uses a new approach to model a tensile test of a high-carbon steel on the basis of discrete element method (DEM). In this research, the tensile test specimen was created by using a DEM packing theory. The particle-particle bond model was used to establish the internal forces of the tensile test specimen. The particle-particle bond model was first tested by performing two-particle tensile test, then was adopted to simulate tensile tests of the high-carbon steel by using 3,678 particles. Findings – This research has successfully revealed the relationships between the DEM parameters and mechanical parameters by modelling a tensile test. The parametric study demonstrates that the particle physical radius, particle contact radius and bond disc radius can significantly influence ultimate stress and Young’s modulus of the specimen, whereas they slightly impact elongation at fracture. Increasing the normal and shear stiffness, the critical normal and shear stiffness can enable the increase of ultimate stress, however, up to maximum values. Research limitations/implications – To improve the particle-particle bond model to simulate a tensile test for high-carbon steel, the damping factors for compensating energy loss from transition of particle motions and failure of bonds are required. Practical implications – This work reinforces the knowledge of applying DEM to model continuous materials. Originality/value – This research illustrates a new approach to model a tensile test of a high-carbon steel on the basis of DEM.

A New Approach for Studying Softening and Melting Behavior of Particles in a Blast Furnace Cohesive Zone

The cohesive zone where ferrous burden materials soften and melt plays a critical role in determining the performance and stability of a blast furnace. The softening and melting behavior of ore particles significantly affects the layer permeability and structure, and subsequently changes the gas/liquid distribution and heat transfer in the cohesive zone. Wax balls are often used in physical experiments to study the ore softening and melting behavior because of their low melting temperature. In this work, a new approach on the basis of discrete element method is established. The relationship between Young’s modulus (E) and temperature (T) of wax balls is first proposed based on the experimental data, and then implemented into a DEM model. The particle deformation, temperature, coordination number, and gas pressure drop under conditions relevant to blast furnace operations are then examined. The results show that the proposed approach can capture the main features of softening and melting behavior of particles. On this basis, the effects of a few variables are investigated. The approach and results should be useful to the establishment of a comprehensive picture about softening and melting behavior, and its effect on blast furnace operations.